Interpol’s Web site (www.interpol.int) went down Tuesday just hours after the international police agency announced the arrest of 25 suspected members of the hacking collective Anonymous in Argentina, Chile, Colombia and Spain.

The authorities in Argentina, Chile, Colombia and Spain carried out the arrests and seized 250 items of IT equipment and mobile phones, Interpol says.Those arrested are aged between 17 and 40.

A National Police statement said two servers used by the group in Bulgaria and the Czech Republic had been blocked.It said the four included the alleged manager of Anonymous' computer operations in Spain and Latin America, who was identified only by his initials and the aliases "Thunder" and "Pacotron".

Authorities in Europe, North America and elsewhere have made dozens of arrests, and Anonymous has increasingly attacked law enforcement, military and intelligence-linked targets in retaliation. Earlier this month the group knocked the C.I.A. Web site offline. A week earlier, the group intercepted a conference call between the Federal Bureau of Investigation and Scotland Yard and released a 16-minute recording of the call.

Spanish police traced back IP addresses from server logs, leading to 10 suspects in Argentina, six in Chile and five in Colombia, responsible for defacement of websites and publishing confidential data, including the personal data of the security detail of unnamed top officials, according to Agence France Presse.

The group had set up a chat-room to help run computer attacks in Spain and Latin America.After the arrests, a call went out in chat-rooms affiliated with the suspects for supporters to attack the Spanish police website. The petition specifically asked for people from outside of Spain to carry out the attacks "so that the police would not have enough data to lead to new arrests", according to the statement.

Anonymous has become increasing politicised over the last year, particularly over issues of online rights and the international controversy over whistleblowing website WikiLeaks.